This invention relates generally to television signal generators, and more particularly to multiple scan rate video test pattern generators for raster scan display devices such as television sets.
Modern television applications are demanding ever greater accuracy in cathode ray tube (CRT) displays. Computer generated images are developed with great timing accuracy and data analysis has been carried to the point that systems are offered in which measurements can be made directly off the television image. Accuracy of placement is paramount in such applications as computerized medical x-ray, industrial process control, etc. This has placed stringent demands on the stability and scan accuracy of television display devices. The response to these demands has been development of more precise television display devices which in turn has led to the need for more precise test techniques and equipment to evaluate a more demanding level of performance.
Television test pattern generators are used to generate a variety of video test patterns which are used to permit adjustment of television receivers or which may be used in the manufacturing and service of television receivers and television signal transmitting equipment.
Examples of test pattern generator systems are disclosed in U.S. Pat. Nos. 4,149,178; 4,093,960; 3,917,902; 3,879,749; 3,019,289; and 4,417,275.
Conventional television test pattern generators require composite, horizontal and vertical blanking, horizontal and vertical drive inputs and provide a composite video signal output.
The television raster is scanned in horizontal lines which progress from the top of the raster to the bottom of the raster. PG,3 After a total raster field has been scanned the process is repeated. In many applications two fields are scanned to complete one "frame" and the fields are "interlaced".
The composite video signal for scanning the television raster is comprised of both picture and synchronizing information. The raster scan synchronizing information consists of horizontal and vertical scan pulses of precisely determined widths and timing. The scan rate can be described on either a time basis or a pixel basis. A pixel is defined as a discreet bit of information corresponding to a discreet picture element.
H drive is a pulse train in which a pulse starts at the end of every television scanning line, its function being to mark the time interval between the end of one line and the start of another line. The H drive pulses may be used to control the horizontal deflection "flyback" and other signal processing. The horizontal drive pulse train is continuous and uninterrupted even during the vertical synchronizing interval. V drive is a pulse train in which a pulse starts at the end of each television field, its function being to mark the time interval between the end of one television field and the next. The V drive pulses may be used to control the vertical deflection "flyback" and other signal processing.
Blanking is a mixture of horizontal and vertical information used to control the "blackout" of a television screen during deflection return or "flyback" between horizontal lines and vertical fields. The blanking pulses are wider than drive and sync pulses in order to insure that all transitions are invisible, i.e. blanked.
Sync is a complex combination of the horizontal and vertical pulse information used to control the decoding of a television signal by the display device, recorder or other type of video processing equipment. Sync is usually mixed with the video information to produce a composite picture signal.
The scan rate is determined by the number of scan lines per field and desired field repetition rate. Most television systems are "interlaced" to avoid a visible flicker in the display, usually at a 2:1 ratio; 2:1, interlaced ratio means that two entire display "fields" must be developed to generate one complete "frame" or image. In the United States, field and frame rates are 60 HZ and 30 HZ respectively, whereas in countries having 50 HZ power, including the European Countries and Japan the field and frame rates are 50 HZ and 25 HZ respectively. Television operation without interlacing, commonly referred to as 1:1 interlace, is also fairly common.
Recently and particularly in the interface of television equipment with computers, there has been a new proliferation of scan rates. There is the never ending search for means to pack more information into a given area at the expense of inactive (blanking) time.
The different types of television systems, e.g. domestic broadcast, foreign broadcast, industrial and military, operate at many different scanning rates. Complete specification of a scan rate requires careful and precise definition of the scan parameters such as the horizontal scanning line repetition rate [usually expressed in kHZ], the number of scanning lines to be developed in each television field, the number of television fields which make up a complete frame, and the widths of the pulses present within the various synchronizing wave forms.
The format of H drive, V drive and blanking is the same for all scanning rates. However, the sync wave form can occur in any one of three formats, namely broadcast, industrial and military. In the broadcast system the vertical sync pulse interval is preceded by a front porch interval and followed by a back porch interval each porch interval having a duration of three scanning line intervals. Six 2H rate equalizing pulses are superimposed on the sync signal during the front porch and back porch intervals, i.e. six equalizing pulses during each such interval, and six 2H rate serration pulses are superimposed on the vertical sync pulse. Domestic broadcast sync also includes horizontal front porch intervals preceding the horizontal sync pulses.
The sync for industrial television is the same as for broadcast television except for the omission of the equalizing pulses and serration pulses. The sync for military television does not include equalizing and serration pulses, has no horizontal front porch, and no horizontal rate pulse information during the vertical front porch interval of three scanning lines.
Conventional sync generator circuits for test pattern generators have been limited in their applicability to test various types of television systems. Typically they provide only one scanning rate depending upon the type of television system with which the test pattern generator is to be used. It is therefore desirable to provide a selectable rate sync generator for universal application to various types of television systems whereby the scanning rate may be selected over a wide range of specifications.
In one prior art patent, U.S. Pat. No. 4,417,275, assigned to the assignee of record of the present application and which is incorporated herein by reference, a selectable rate sync generator system is provided which selects the desired scan rate by specifying the total horizontal line time and the number of scan lines which are to occur in two fields, regardless of the number of fields which make up a frame. The horizontal repetition rate is either specified or can be calculated. The calculated horizontal line time is selected by a total horizontal line time thumb wheel selection switch which results in the desired horizontal rate. Another thumb wheel selection switch in the system is set for the desired number of scan lines in two fields.
Signal source 1206A, which is a pattern generator and sync generator manufactured by Visual Information Institute, Inc., the assignee of the present application, utilizes a plurality of switches to set various parameters for generation of the synchronizing waveform and pattern. This device and the accompanying technical manual therefor is incorporated herein by references.
A problem with the prior art sync generator test systems has been that, in pixel based rasters, the number of horizontal lines per field and the line time needed to be calculated. This process was time consuming and unwieldy. Furthermore, in such systems the oscillator frequency had to be varied to accomodate the different system requirements, whereby an infinitely variable oscillator had to be provided. This requirement placed special demands on the system designer. It is therefore desired to provide a sync generator for producing variable scan rates with a fixed frequency oscillator.
While the raster scan test pattern generator described in the above-identified prior art U.S. Pat. No. 4,417,275 is satisfactory for many applications, it is desirable to provide a test pattern generator which is readily applicable to television systems wherein the rasters are defined in pixels or number of data bits per horizontal line without the need for multiple calculations in the use of the generator.
One prior art pixel based sync generator system has been provided wherein a frequency synthesizer is used comprising a variable oscillator having a variable frequency. The system requires entry of a few major parameters defining a scan rate and then calculates all values for the desired scan rate. The disadvantage of the system is that binary integers must be used for computing the different frequencies, whereby certain frequencies cannot be provided with the system and certain raster specifications will not be achievable. Additionally, the lack of sufficiently fine resolution achieved with that system at the higher frequency ranges of the oscillator is undesirable.
What is therefore desired is to provide a universal time based sync generator system wherein multiple scan rate test patterns, both time and pixel based, can be generated by entering the parameters for all the horizontal and vertical sync pulse elements into a keyboard and wherein the system builds or generates the scan rate from the discrete defined sync elements.
Another disadvantage of the above-identified prior art pixel based sync generator system is that all entries must be made on the keyboard or keypad. Thus with that system, if a television unit were being tested and several different patterns were desired to be viewed, such as a bar pattern, a dot pattern, gray scale, etc., this could not be quickly achieved as new entries would have to be made in the keyboard. What is therefore desired is a sync generator system wherein the parameters for a particular scan rate are preset in a keyboard and wherein a control is provided which permits rapid selection of different types of test patterns which are generated utilizing the scan rate parameters keyed into the keyboard.
What is also desired is a sync generator wherein stored raster scan test patterns can be altered and customized as desired.
What is furthermore desired is a sync generator wherein stored raster scan test patterns can only be altered by entering a software security code into the keyboard.
What is still further desired is a test pattern generator which provides a default scan rate when the system is first turned on, whereby a predetermined raster scan rate is provided to prevent any damage to the Cathode Ray Tube unit being tested.
What is yet further desired is a sync generator system having a keyboard display for displaying parameters and other items in a user friendly readable language rather than digital code.